1. Field of the Invention
This invention relates to an image capturing apparatus and a method therefor, and more particularly, is suitably applied, for example, to a video camera.
2. Description of the Related Art
Conventionally, there is a video camera which composes a plurality of images captured with different amounts of exposure to produce an image having a wide dynamic range (i.e., an image which represents from a light region to a dark region).
A method of capturing a plurality of images with different amounts of exposure as mentioned may employ, as an imager device, a solid-state imager device (CCD: Charge Coupled Device), and involves adjusting an electronic shutter, which is a function possessed by the CCD, to change the exposure time to capture a plurality of images in a time division manner. In this method, a charge is accumulated and read in an arbitrary field period in a manner similar to a normal imaging operation, and subsequently a charge is again accumulated and read utilizing a vertical blanking period to capture two different images with different exposure times within one field period.
Also, as illustrated in FIG. 1, another method utilizes Neutral Density (ND) filters 3 having different transmittivities placed on respective pixels of an imager device 1 to capture an image which is spatially divided into segments having different amounts of exposure. Further, as illustrated in FIG. 2, another method involves providing a plurality of imager devices 5A, 5B, and capturing a plurality of images without reducing the spatial resolution by disposing ND filters in front of the respective imager devices, for example, placing an ND filter 7 in front of the imager device 5B, to give different transmittivities.
The method of capturing a plurality of images having different amounts of exposure in a time division manner is capable of producing an image of higher resolution as compared with the method of capturing a plurality of images having different exposure amounts in a spatial division manner, and is simpler in structure and lower in cost as compared with the method of capturing a plurality of images having different amounts of exposure using a plurality of imager devices. It can therefore be said that this image capturing method is better than the other two.
However, since the method of capturing a plurality of images having different amounts of exposure in a time division manner captures respective images having different amounts of exposure at different times, misregistration between the respective images, if caused by unintended movements of hands or the like, would result in a problem of a degraded image quality on a resulting composite image produced by composing the captured images having different amounts of exposure due to the misregistration on the composite image.
Referring now to FIGS. 3A and 3B, explanation will be given, of how such misregistration between respective images causes a degraded image quality of a composite image. FIG. 3A one-dimensionally shows an image captured with long time exposure; and FIG. 3B one-dimensionally shows an image captured with short time exposure, where misregistration equal to a length D occurs between the two images. When these two images are composed, disturbed image portions will be produced near the edges, as a composite image shown in FIG. 3C.